FILE: A bitcoin token sits next to the image of George Washington on a U.S. one dollar bill in this arranged photograph in London, U.K., on Wednesday, Jan. 4, 2017. The great cryptocurrency crash of 2018 is heading for its worst week yet. Bitcoin sank toward $4,000 and most of its peers tumbled on Friday, extending the Bloomberg Galaxy Crypto Indexs weekly decline to 25 percent. Thats the worst five-day stretch since crypto-mania peaked in early January. Photographer: Chris Ratcliffe/Bloomberg via Getty Images

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